This invention relates to a state information communicating system which is for use in a TDMA (time division multiple access) satellite communication network.
It is a recent trend that a TDMA satellite communication network is widely applied to various communications, such as a domestic communication, a business communication, and the like. The satellite communication network comprises a plurality of terrestrial or earth stations and at least one standard earth station. The standard earth station is for periodically generating standard bursts. Each standard burst defines a TDMA frame consisting of each standard burst and a remaining part. The remaining part comprises a first and a second part. The first part is for data bursts produced by the terrestrial stations and the standard earth station. Each of the data bursts includes a traffic data to be communicated. The second part is a remaining part of each frame.
In the TDMA satellite communication network, each of the terrestrial stations is a nonattendant station in general. Therefore, it is general that supervision of the terrestrial stations is remotely and automatically carried out at the standard earth station. For this purpose, each terrestrial station sends a set of state information signals which are representative of the states of operation of the terrestrial station under consideration. The "states of operation" must be monitored to detect, for example, indications of alarm conditions relating to communication devices and associated equipment, selection status of redundant equipments, data collected by built-in test capability, room temperature, maintenance condition, and the like.
In a conventional state information communicating system which will later be exemplified more in detail, such a set of state information signals are sent from the respective terrestrial stations by the use of state information time slots of the TDMA frame. The state information time slots are specific to the respective terrestrial stations and are assigned thereto, all in a part of the second part.
In each TDMA frame, a standard burst time slot for the standard burst and the state information time slots do not carry any traffic data. In view of this fact, it is possible to define as regards each TDMA frame a ratio of a total time slot used for traffic data to the TDMA frame. The ratio may define a frame availability. It is desirable that the frame availability is as high as 95% or 98%.
The conventional state information communicating system is unsuitable to achieve such a high frame availability. This is because the state information time slots are included in each TDMA frame for the respective terrestrial stations.
In order to achieve a high frame availability, it is desirable to shorten the state information time slots in each TDMA frame. To this end, it may be considered that each terrestrial station divides the state information signals into many divisions and sends the divisions by the use of narrow state information time slots in a plurality of TDMA frames, respectively. It should be noted that each of the state information signals, which is representative of each state of operation, is not necessarily composed of a single bit, but may also be composed of several bits. This means that each division itself cannot completely include each state information signal and therefore may not have significant meaning. In this case, the standard earth station has to receive and collect all of the divisions for each terrestrial station and to assemble the divisions into significant words, each of which is representative of at least one state of operation. Therefore, the standard earth station needs a complicated processing device in order to assemble the divisions.